1. Field of the Invention
The present invention relates to an optical disc device for recording data on a recordable optical disc. The invention also relates to a tracking control method.
2. Description of the Related Art
For current optical disc devices, during data recording on a recordable optical disc (such as a CD or a DVD), there is a need to prevent erroneous erasure of recorded data from adjacent tracks due to a tracking servo control error (hereinafter, called ‘off-servo’ or ‘off-tracking’). Accordingly, these devices have a function that monitors the amplitude of tracking error (TE) signals and if a TE amplitude threshold level is exceeded for a predetermined time, judges off-tracking to have occurred, and conducts a process, for example, to immediately stop the recording operation.
With regards to the threshold level for the off-tracking judgment in the above case, a trifle high level is assigned for DVD-R's and other discs on which data can be recorded one time only. Otherwise, abortion of the recording operation in progress will make the disc itself no more usable. This is why the high threshold level is assigned to prevent off-tracking from being detected more often than necessary. An independent threshold level is assigned for off-tracking detection during playback. For example, since playback, unlike recording, can be easily retried, a threshold level lower than that of off-tracking detection during recording is assigned for easier detection of off-tracking. Conversely in some cases, the threshold level for off-tracking detection during playback is higher than that of off-tracking detection during recording.
After receiving a recording command, such an optical disc device moves an optical head to the vicinity of a recording position on the disc during seek operation, then moves the head to the starting position of recording, and starts to record data. The device detects the starting position of recording, by reading a recording start address from a wobble signal (or the like) provided on the recording disc. During this reading operation, the device uses a common threshold level to detect off-tracking.
In addition, with the progress of high-speed recording by optical disc devices, there is a need to build in an off-tracking detection function more efficiently. For example, JP-A-2004-310911 discloses a device having servo-off detection means and adapted so that even when the servo-off detection means is effective, the device can rapidly start recording and so that even during recording, the device is able to sense an off-servo error in advance and to record data at high speed without causing off-servo. Hence, the device classifies servo signal error counts according to threshold level and selects the optimal recording speed for the particular error level of the servo signal.